In measuring devices with comfortable display possibilities or in measured data processing systems it is frequently required to spatially separate the measured value pick-up including the actual physical-to-electrical transducer from an evaluating circuit or device for measured signal processing. Thereby, the measured value pick-up and the evaluating circuit are, as a rule, connected to each other by electrical conductors. The electrical conductors must partially bridge distances of a few hundred meters. However, frequently it is only the environmental influences which require a spatial separation of the measured value pick-up from the evaluating devices. Particularly in connection with such spatial distances it is thus required that the evaluating devices are adapted to the correct characteristic and calibration values of the physical-to-electrical transducers in order to make possible a standardized measured value display or a further processing.
For these purposes numerous measured values pick-ups are realized with an analog electric interface. This applies particularly to pick-up methods in which the measured value is transformed at the pick-up without active electronic circuits into an electrical signal, whereupon the signal processing takes place in a separate circuit or in the evaluating device. In this case the characteristic values of the physical-electrical transducer or pick-up are held generally in a separate data sheet or in a calibration protocol. This information is necessary in any case in a separate circuit or in the evaluating device for the interpretation of the output signal of such a measured values pick-up and for the coordination of the physical measured value to the output signal. For this purpose these characteristic values must be entered mostly manually into the separate circuit or into the evaluating device. Such manual entering may, in practice, lead to erroneous entries or to confusing the corresponding data sheets. Thus, quite a number of pick-ups with connected electronic circuits are known in which the data sheet information or the calibration characteristic values of the pick-ups are permanently stored. The permanently stored information and values can be read-out by the connected evaluating device.
An electrical connector plug with an electronic data carrier is known from German Patent Publication DE 41 14 921 C2. The connector plug is connected with a temperature sensor as a physical-electrical transducer through four electrical conductors. Eight plug pins are provided in the electrical connector plug for transmitting the measured values and the characteristic values stored in the electronic data carrier to an evaluating device through these plug pins. Thereby, the memory is connected through four separate plug pins which are not needed for the measured signal, to the evaluating device. Thus, where there is a larger spatial distance between the thermoelement with its electrical connector plug and the evaluating device, separate conductors for the transmission of the characteristic values into the evaluating device would have to be provided. Such separate conductors entail a higher effort and expense for conductors, particularly for connecting a larger number of pick-ups to one evaluating device. Such extra conductors are frequently hard to integrate into present testing set-ups.
A pick-up for measuring physical values is known from EP 0,233,176 B1. The physical-to-electrical transducer of this pick-up is integrated into a structural unit with a programmable not volatile electronic memory for correction data. Thereby, the electrical pick-up signals and the memory data are supplied at a common output in a timed sequence to an evaluating circuit. The electronic circuit comprised in the pick-up structural unit is thereby so constructed that the measured data are converted prior to the transmission from analog-to-digital. EP 0,233,176 B1 does not describe in detail how the transmission of a strictly analog measured signal and of the memory data to a common output can be realized.
A further measured value pick-up is known from European Patent Publication EP 0,324,067 A2 which comprises measuring transducers in a bridge circuit and an integrated parameter source. The parameter source comprises an electronic memory circuit in which pick-up characteristic or correction values are programmably stored and from which these pick-up characteristic or correction values can be read-out in serial fashion. These pick-up characteristic or correction values can be read-out or can be newly programmed by an evaluating device through two measuring or power supply conductors. For this purpose the read-out procedure is controlled through a special third conductor between the pick-up and the evaluating circuit. The third conductor serves for initiating the read-out process for the correction data or for the measured value transmission. However, when using such pick-ups one more connecting conductor is required in any case for the characteristic value transmission compared to a conventional pick-up with analog interfaces. Thus, in connection with available measuring circuits an exchange of conventional pick-ups for pick-ups with a characteristic value read-out is not possible.
A measuring pick-up is known from European Patent Publication EP 0,541,573 B1 which pick-up is basically a further development of the pick-up according to EP 0,324,067 A2. In that measured value pick-up a so-called shunt control conductor is used for the control of the characteristic value transmission between the memory circuit and the evaluating device. Such a conductor is customarily present in certain types of pick-ups such as acceleration pick-ups. The measured value pick-up of EP 0,541,573 B1 thus describes a possibility to connect such a parameter source or its memory circuit to an evaluating device without additional conductors. However, in connection with measured value pick-ups which do not have such a shunt control conductor, this method is not useable or an additional control conductor is required.